Long Term Evolution (LTE) is the name given to a project to improve the Universal Mobile Telecommunications System (UMTS) standard to cope with future requirements. In one aspect, UMTS has been modified to provide for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) as a fourth generation (4G) wireless network.
An E-UTRAN includes eNodeBs, which provide the Evolved Universal Terrestrial Radio Access (E-UTRA) user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations with a user equipment (UE). The eNodeBs are interconnected with each other by an X2 interface. The eNodeBs are also connected to a Mobility Management Entity (MME) via an S1-MME interface, and to a Serving Gateway (S-GW) via an S1-U interface.
Within an E-UTRAN, Multimedia Broadcast Multicast Service (MBMS) is a multicast (point-to-multipoint) service in which multimedia content (e.g., voice, audio, video, etc.) is transmitted from an MBMS gateway (MBMS GW) to multiple eNodeBs and then to multiple UEs with the help of a Multi-cell/Multicast Coordination Unit (MCE). Broadcast/multicast transmitting of the same content to multiple UEs using a relatively small amount of network resources (rather than using multiple network resources for the same content) reduces system resource utilization, which improves overall system performance because the conserved network resources may be used for other traffic.
FIG. 1 shows a portion of a conventional E-UTRAN deployment including an E-UTRAN access gateway 100 in communication with a plurality of eNodeBs 105. The E-UTRAN in FIG. 1 provides MBMS to UEs within the E-UTRAN. As discussed herein, eNodeB refers to a base station that provides radio access to UEs within a given coverage area. This coverage area is referred to as a cell. However, as is well-known, multiple cells are often associated with a single eNodeB.
The E-UTRAN access gateway 100 includes an MBMS Multi-cell Coordination Unit or Entity (MCE) 110 and an MBMS GW 112. The MBMS MCE 110 is a logical entity that controls the eNodeBs 105 and coordinates multi-cell scheduling and transmission for eNodeBs 105 belonging to the same Multimedia Broadcast Single Frequency Network (MBSFN) area, which will be discussed in more detail later. In more detail, functions of MBMS MCE 110 include scheduling and timing control, eNodeB registration and feedback. The MBMS GW 112 is a logical entity that multicasts MBMS packets to each eNodeB providing the MBMS.
As is well-known, an MBSFN area is comprised of a group of cells that form a MBSFN Synchronization Area of a network. In the MBSFN Synchronization Area, the group of cells are synchronized and coordinated to perform MBSFN transmissions. An MBSFN transmission is a simulcast transmission technique in which identical waveforms are transmitted from multiple cells at the same time. A MBSFN transmission from multiple cells within the MBSFN area is seen as a single transmission by a UE, where the UE automatically combines the E-UTRAN's orthogonal frequency division multiplexed (OFDM) signals from multiple adjacent cells to improve reception resulting from improvements in signal to noise ratio (SNR).
The E-UTRAN access gateway 100 further includes a mobility management entity (MME) 140 in two-way communication with the eNodeBs 105. As described in 3GPP TS 36.300 V.8.6.0, the entire contents of which is incorporated herein by reference, the MME 140 controls, inter alia, user radio access network (RAN) mobility management procedures and user session management procedures.
For example, the MME 140 controls a UEs tracking and reachability. The MME 140 also controls and executes transmission and/or retransmission of signaling messages such as paging messages for notifying destination UEs of impending connection requests (e.g., when UEs are being called or when network initiated data intended for the UE is coming).
In performing its mobility management functions, the MME 140 stores a tracking area (TA) or list of tracking areas for each UE when the UEs are in the RRC_IDLE mode. The TA includes a plurality of cells located in close proximity to one another and indicates the area in which the UE is located. This location information is refreshed through a “location update” message (e.g., the Tracking Area Update (TAU) Message defined in 3GPP TS 36.300 V.8.6.0) sent by the UE either periodically or when the UE's tracking area changes.
When the MME 140 is notified of a connection request for a UE, the MME 140 sends a paging message to each eNodeB within the UE's tracking area. These paging signaling messages, which are part of the S1-AP layer in the protocol stack, are passed from MME 140 to each eNodeB in the UE's tracking area over a separate, point-to-point S1-MME interface. As a result, identical messages are sent over multiple point-to-point links to each eNodeB in the UE's tracking area.
In response to receiving the paging messages, the eNodeBs broadcast the paging messages on a slower signaling control channel such as the Paging Control Channel (PCCH) or Broadcast Control Channel (BCCH). These control channels broadcast the signaling messages to the entire coverage area of the cell. Conventionally, the slower signaling control channels are used because the data rate is limited for UEs near edges of cells due to their distance, inter-cell interference, as well as the use of lower code rate and lower level of modulation (e.g., quadrature phase shift keying (QPSK)).
As is well-known, the air interface resources are critical resources for a service provider. When a plurality of cells are used for transmitting the same content at a slow data rate, significant amounts of the air interface resources are wasted. This slow and costly signaling procedure is a potential weakness for any wireless network.
In most cases, especially during busy hours, many UEs in the same tracking area may need to be notified of connection requests at about the same time. As a result, the unicast signaling (in which identical messages are sent over separate, multiple point-to-point links) occurs many times (once for each UE) within a small time period depending on the typical discontinuous reception (DRX) cycles for UEs. When this occurs, similar packets are repeated at an unnecessarily high rate across connections for various network entities (e.g., MME to each of a plurality of eNodeBs). The service provider normally bears the burden of this consumption of network resources.
The transmission of these identical signaling messages to UEs over the air interface at slower data rate by all cells in a tracking area also wastes critical system resources and results in some degradation due to over-usage of system resources for the signaling messages that do not contribute to revenue generation.
Moreover, it is well-known that UEs may experience a ‘ping-pong’ effect near boundaries between tracking areas because the UEs capable of registering with either one of the two adjacent tracking areas may toggle between the two due to dynamic changes in radio frequency (RF) conditions. This ping-pong effect consumes unnecessary resources because messages must be transmitted through the air interface and pass through the distributed network entities each time the UE toggles between the adjacent tracking areas.
Further, once a UE is notified of an incoming connection request (via a paging message), the UE and the radio access network (RAN) exchange messages to setup a connection with an evolved packet system (EPS) default bearer. The EPS default bearer is normally a best effort Internet Protocol (IP) connection. The actual IP services requested (e.g., for a voice call over IP) are communicated only after setting up the initial connection. The specific application(s) involved are then started and their associated dedicated EPS bearers with specific quality of service (QoS) are established. In this instance, some undesirable delay exists and impacts the wireless user's experience for both the calling user and the called user.